There are several models of Browning .50 caliber machine guns. Among these are the models M2HB, M3HB, M3HB flexible, M3, and M3M. An example of the M2HB model machine gun 2 is shown in FIG. 1.
The various M2 and M3 models include a trunnion 4 in the front of the receiver 6 of the machine gun 8 (see FIGS. 2A and 2B). Referring to FIGS. 3 and 4, there is shown a trunnion 4. The trunnion 4 has a large pintle receiving hole, e.g., hole 10, on each of its side faces, e.g. face 12. Referring to FIG. 4, these receiving holes are for receiving a pintle 14 for moveably securing the machine gun 8 to the cradle of a gun support 16. Referring again to FIG. 3, the trunnion 4 has a cylindrical nose 18 which is both internally and externally threaded at its distal end 20. These threads are provided for connecting a barrel support to the receiver for axially supporting the barrel of the machine gun. FIG. 4 shows an example of a large diameter barrel support 22 that is threaded onto the outer threads of the trunnion 4. FIG. 5 shows an example of a small diameter barrel support 24 that is threaded onto the inner threads of the trunnion 4.
The various M3 models are used primarily on helicopters and gunships. For this purpose they are often provided with a trunnion adapter that fits onto the nose of the trunnion which permits them to fit into the cradles of the gun supports which are provided in such vehicles. The trunnion adapters are used because the pintle receiving holes of the trunnion are ill-positioned to receive the pintles of the gun supports of helicopters and gunships. FIGS. 6A and 6B show, respectively, front and side views of such a trunnion adapter 26. The trunnion adapter 26 is internally threaded to thread onto the outer threads of the trunnion nose 18 (see, e.g., FIG. 3). The trunnion adapter 26 also has and a yoke 28 having pintle receiving holes 30, 32 for receiving the pintle of a gun support. The trunnion adapter 26 is used in conjunction with a small diameter barrel support, e.g. barrel support 24 (see FIG. 5).
Such trunnion adapters have been in use for over half a century. The problem with the trunnion adapters that has persisted all this time is that they prevent the guns on which they are used from being mounted on many types of gun supports because their yoke sections interfere with structural members of the gun supports. Although the trunnion adapters may be removed from these guns to permit use of the gun on the gun supports by way of the pintle receiving holes of the trunnion, this solution has its drawbacks in that it leaves the outer threads of the trunnion nose exposed to damaging impacts which could render them unusable. Once they are unusable, the machine gun is no longer capable of receiving a heavy barrel support or of receiving a trunnion adapter.